The present invention relates to a combustion state detection system for an internal combustion engine (hereinafter sometimes referred to as xe2x80x9cthe enginexe2x80x9d), or more in particular to a combustion state detection system for an engine capable of positively detecting a misfire occurring in an operation area resonating with the natural frequency of the vehicle body.
A conventional technique, as disclosed in Japanese Patent Application Publication No. JP-A-58-51243, is well known, in which the engine operating condition is detected by measuring the engine speed and detecting an engine misfire indirectly, taking advantage of the relation between the torque generated by the engine and the engine speed. In this conventional technique, the engine speed is detected at least at two ignition points within one ignition cycle from the previous ignition point to the current ignition point, the engine speed change in the ignition cycle is determined from the difference in engine speed, engine speed changes sequentially determined are statistically processed, and the engine combustion state is judged using the result of the processing.
The above-mentioned conventional technique is effective in the case of detecting a misfire when the engine is running at a comparatively low speed under a small load. In the case where the engine is running at a low speed under a heavy load, however, the speed change signal generated at the time of engine misfire resonates with the natural frequency of the vehicle body, thereby causing a secondary vibration. In the case where an overshoot of this secondary vibration signal exceeds a level of a misfire judgement, the engine is regarded to have caused a misfire, often causing a diagnosis error inconveniently.
On the other hand, Japanese Patent Application Publication No. JP-A-7-19090 discloses means for detecting the engine combustion state by measuring the engine speed taking advantage of the relation between the torque generated by engine combustion and the engine speed. This conventional technique also discloses a technique for protecting against variations in the engine speed signal not related to the change in the engine combustion state at low engine speed under heavy load leading to the resonance between the power train and the engine of the vehicle. This conventional technique is intended to inhibit a specific control (feedback control of the air-fuel ratio) in the case where the engine speed signal not related to the change in the engine combustion state undergoes a change, but discloses no technique for detecting the true change in the combustion state of the engine running at low speed under heavy load which may involve an engine speed signal not related to the change in the combustion state. The problem still remains to be solved, therefore, for detecting the engine combustion state at low speed under heavy load.
The present invention has been developed with the intention of solving the above-mentioned problem, and the object of the invention is to provide a combustion state detection system for an internal combustion engine, in which the combustion state in all the operating areas of the engine can be detected, and especially, the combustion state in the operating area where an engine speed change signal resonates with the vehicle vibrations and causes a secondary vibration is positively detected thereby to improve the detection accuracy of an engine misfire.
In order to achieve the above-mentioned object, according to one aspect of the invention, there is provided a combustion state detection system for an internal combustion engine, in which the engine combustion state is basically detected by combustion state parameters calculated from a timing signal associated with the rotation of the crankshaft by a predetermined angle, comprising means for compensating for the combustion state parameters and combustion state parameter compensation permitting condition determining means for permitting or inhibiting the execution by the combustion state parameter compensation means.
According to a specific preferable aspect of the invention, there is provided a combustion state detection system for an internal combustion engine, in which the combustion state parameter compensation means is a reverse model for offsetting the vibrations of the combustion state parameter generated by the resonance with the natural frequency of the vehicle body, in which the vibration model of the combustion state parameter is approximated to the transfer function of the secondary vibration system, in which the pole of the transfer function of the vehicle body vibration is offset at the zero point of the transfer function thereby to prevent the resonance of the combustion state parameter due to the vehicle body vibrations, and in which the combustion state parameter compensation means is a band-cut filter.
According to another aspect of the invention, there is provided a combustion state detection system for an internal combustion engine, in which the means for determining the conditions for permitting the combustion state parameter compensation determines such conditions from the operating condition parameters based on the function of the engine speed and the engine load.
According to still another aspect of the invention, there is provided a combustion state detection system for an internal combustion engine, further comprising a combustion state judging means for comparing the combustion state parameter with a specific decision level thereby to detector a misfire.
According to yet another aspect of the invention, there is provided a combustion state detection system for an internal combustion engine, further comprising a means for judging the conditions for permitting the combustion state parameter compensation, and a combustion state parameter compensation means, wherein whether the engine operating conditions are in an area of a low speed and a heavy load including an engine speed signal not related to the change in combustion state, and wherein the combustion state parameter can be compensated for in the case where the engine operating conditions are in such an area.
According to a further aspect of the invention, there is provided a combustion state detection system for an internal combustion engine, in which the vibration mode of the engine speed signal can be approximated to the secondary vibration system in a low-speed, heavy-load area where the engine speed signal resonates with the natural frequency of the vehicle body, and therefore the secondary vibration mode is offset for compensation, so that the true change in the engine combustion state of the internal combustion engine can be detected even in a low-speed, heavy-load area including the engine speed signal not related to the change in the engine combustion state.
Consequently, the combustion state parameter thus compensated is compared with a specific decision level by the combustion state judging means, thereby making it possible to detect an engine misfire in all the operating areas of the internal combustion engine.